This invention relates to control systems for a vehicle, and more particularly, to a control system for an excavator wherein hydraulically operated means are provided for swinging the machinery platform and for driving the vehicle.
In a vehicle of the type wherein a machinery platform is swung relative to the lower frame of the vehicle, it is well known to provide a hydraulic circuit for the actuation thereof. In such a typical circuit, a hydraulic pump may be selectively communicated with a hydraulic motor to drive the swing motor in one and the other directions as required, to in turn swing the machinery platform in one and the other directions. In such a system, it is generally provided that in the state wherein swinging does not take place, the swing pump communicates with tank. Thus, in such state, the swing pump is not being used. It should also be understood that in such a system the overall percentage of time that the swing pump is being used is quite small, in relation to the overall operating time of the apparatus. Such swing apparatus, for example, would not generally be used as the vehicle is driven over the ground.
Of general interest in this area is U.S. Pat. No. 3,476,274 to Witwer, disclosing a system wherein hydraulic fluid from the portion of the hydraulic system employed for swinging the machinery platform is diverted to hydraulic ram means which operate the boom or dip stick. Also of interest is U.S. Pat. No. 3,759,357 to Bianchetta (assigned to the assignee of this invention), disclosing a brake control system in conjunction with a drive control system of a vehicle. The present inventive fluid circuit incorporates the system of U.S. Pat. No. 3,759,357, which will be described in detail.